Thank you for reporting a problem. I deleted another post you put that was somehow duplicated.

Please, make sure of this:* Ensure that you download the correct version for your operating system (Linux in this case) and that you use the correct architecture (32 or 64 bit) depending on your operating system and Blender version.

* Try using YafaRay combined with the blender 2.78c downloaded from blender.org website and not the one coming with the Ubuntu distribution.

* Make sure there are no other YafaRay versions anywhere in the Blender addons folder. There are several possible locations for the Blender addons folder, for example it could be in /usr/share/blender/scripts/addons and also in $HOME/.config/blender/2.78/scripts/addons Remove any previous versions of YafaRay from all of them.

* Make sure there are no other YafaRay forks such as The Bounty renderer in those locations as well.

Before I create this topic, I reinstalled Blender and deleted everything in 2.7x folders founded on my HDDs.I download newest (2.78c) Blender version and YafaRay.v3.2.0.build.for.Blender.2.78.for.Linux.64bit.zip

Any other ideas? BTW: It's not highly important for me, I just want to try it, so if you manage to find time for this I'll be thankful. If not, no problem, never mind.

In a virtual machine, I've installed Ubuntu Studio 64bit, then downloaded Blender 2.78c for Linux 64bit from blender.org, downloaded the YafaRay v3.2.0 for Linux 64bit, installed the yafaray zip file using Blender User-Preferences Add-Ons page, enabled it and used it without a problem.

Please take a good look. Maybe you have a YafaRay fork such as TheBounty? If yes, please remove it as well.